Growing & Winemaking


Best Practices for Gas Management at Bottling

October 2017
by Magali-Eve Koralewski

Total package oxygen (TPO) management at bottling is crucial to avoid wine oxidation. According to bottling audits performed around the world, average TPO is 3 parts per million (ppm). This one-shot addition of 3 ppm at bottling may seem rather small, but when compared to what a closure brings per year—1 mg of oxygen in the case of a Nomacorc Select Green 100, for example—this potentially corresponds to three years of shelf life. It is important to take good care of TPO and develop strategies to control it in a consistent manner across the bottling process.

Both dissolved oxygen (DO) in the wine and headspace oxygen (a function of oxygen percentage in the headspace and headspace volume), when combined, are the definition of TPO.

How can low TPO be achieved? A key point is to measure O2 regularly at different bottling steps. Measuring TPO regularly is the only way to accurately quantify critical oxygen pickup and identify TPO variations during the process. The most recognized way to measure it is to use the NomaSense O2 P300 analyzer and a piercing system designed to facilitate real-time TPO measurements. 

Based on hundreds of bottling audits performed around the world, we developed a specific quality-control approach both on gas-management and bottling-line settings in order to help wineries achieve best-in-class bottling practices.

Start with a low dissolved oxygen concentration in wine
To achieve the lowest TPO, the first point to check is dissolved oxygen concentration in wine before the start of bottling. Measurement can be done directly in the tank with an immersion probe or using an oxygen sensor glued in a sightglass, allowing for a measurement during wine transfer. Our recommendation is to have a DO lower than 0.5 ppm in the tank. If higher, previous wine preparation steps (tartaric stabilization, filtration, etc.) may need to be better controlled and managed. Measurement can be done during these steps in order to identify where oxygen pickup occurs and then develop strategies to minimize pickup. Deoxygenation of the wine can be a solution to decrease DO, but it has to be well executed without being detrimental to wine quality.

Perform DO and CO2 measurements at start of bottling
The beginning of the bottling process can be a critical step for oxygen pickup. Hoses, the pump, filter, filler bowl and bottling line circuits are full of air and can generate consequent oxygen dissolution in wine and a large variation between bottles filled at the beginning of the run. At this stage of the process, both O2 and CO2 measurements are recommended to ensure better bottle-to-bottle consistency. Bottles of wine at the beginning of the bottling process often have more DO and less CO2.

If high oxygen dissolution occurs, CO2 loss can be important and generate a real impact on the aromatic profile, depending on wine style. DO control can be achieved after the pumps, the filters and before the filler bowl using a sightglass. Then final measurement can be performed directly using specially prepared sealed test bottles with sensors glued inside them.

To avoid high DO levels and losses of dissolved CO2, the use of inert gas (preferably a mix of nitrogen and CO2 gases to retain the intended CO2 level in wine) is recommended before priming the line. Even so, check the efficiency of the inerting method by measuring the O2 level in hoses and the whole circuit to confirm it has been decreased to less than 2% before starting to pump wine into the system. Another solution, depending on the bottling equipment, is to empty the first filled bottles back into the bottling tank to get a better consistency throughout the run.

Check filling system performance
Once priming is done, checking of each filling valve and the inerting system of the empty bottle (if installed on the line) can be performed in order to assess the filling performance of the equipment. Both consistency and oxygen pickup can be assessed. Inerting of the empty bottle before filling can reduce DO as much as 0.5 ppm. With new equipment and/or good settings, the level can be very low, with a pickup below 0.5 ppm. DO variation between bottles has to be as low as possible, and we recommend less than 0.3 ppm difference as a target. In the end, DO in bottled wines should be lower than 1 ppm. 

Manage headspace oxygen level and consistency
Oxygen in the headspace (HSO) is another critical point during bottling. According to our data, it usually represents more than 50% of the TPO, which makes it the biggest reservoir of oxygen in a bottle. This is the biggest source of bottle-to-bottle variation. HSO measurement after corking is crucial to assess pickup and variability levels. In case of cylindrical closures, the use of a vacuum system before corking is common practice to reduce the HSO level, but even with a good vacuum system the HSO would still be around 8%-10% oxygen. If coupled with inert gas injection, the HSO level can be decreased further, and bottles will contain as little as 0.2 ppm in the headspace.

With screwcaps, the headspace volume is generally bigger, and a vacuum system cannot be used. As a consequence, these bottles generally contain higher HSO levels. In the best case, a generic inerting system can help reduce the average HSO level in screwcapped bottles from 5-6 ppm to 2-3 ppm, which is still quite high regarding post-bottling shelf-life management. To get a better HSO level in screwcapped bottles, we recommend using a system that has a double inert gas injection both inside the screwcap and bottleneck.

TPO calculation and corrective actions
Once HSO measurement is completed, TPO calculation can be performed to obtain an overall view of bottling line performance in terms of oxygen management. Vinventions recommends that the TPO should be less than 2 ppm for conventional wines and less than 1 ppm for low-sulfite wines.

Thanks to each oxygen measurement done at the different steps of the bottling process, critical pickup stages can be identified and optimized. Even when best-in-class practices are in operation, frequent measurement remains necessary, as the right quality-control tool to en sure that the bottling line performance is always at its best. 

Magali-Eve Koralewski is an enologist who joined Vinventions in April 2014 as the enology department’s technical writer to create technical content and communications from enological research and innovations developed by Vinventions’ enology team. She previously spent six years as a journalist and chief of the enological rubric for Réussir Vigne, a French magazine specializing in viticulture and enology. 

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